Type One Protein Phosphatase 1 and Its Regulatory Protein Inhibitor 2 Negatively Regulate ABA Signaling

Abstract

The phytohormone abscisic acid (ABA) regulates plant growth, development and responses to biotic and abiotic stresses. The core ABA signaling pathway consists of three major components: ABA receptor (PYR1/PYLs), type 2C Protein Phosphatase (PP2C) and SNF1-related protein kinase 2 (SnRK2). Nevertheless, the complexity of ABA signaling remains to be explored. To uncover new components of ABA signal transduction pathways, we performed a yeast two-hybrid screen for SnRK2-interacting proteins. We found that Type One Protein Phosphatase 1 (TOPP1) and its regulatory protein, At Inhibitor-2 (AtI-2), physically interact with SnRK2s and also with PYLs. TOPP1 inhibited the kinase activity of SnRK2.6, and this inhibition could be enhanced by AtI-2. Transactivation assays showed that TOPP1 and AtI-2 negatively regulated the SnRK2.2/3/6-mediated activation of the ABA responsive reporter gene RD29B, supporting a negative role of TOPP1 and AtI-2 in ABA signaling. Consistent with these findings, topp1 and ati-2 mutant plants displayed hypersensitivities to ABA and salt treatments, and transcriptome analysis of TOPP1 and AtI-2 knockout plants revealed an increased expression of multiple ABA-responsive genes in the mutants. Taken together, our results uncover TOPP1 and AtI-2 as negative regulators of ABA signaling.

Protein phosphatase type 2C PP2CA together with ABI1 inhibits SnRK2.4 activity and regulates plant responses to salinity

“…This mechanism of PP2Cs inhibition is strongly dependent on ABA. It was recently shown that also Type One Protein Phosphatase 1 (TOPP1) regulates the activity of ABA-activated SnRK2s, 20 and it was proposed that regulation of TOPP1 activity and subsequently that of SnRK2s was dependent on PYL11 and ABA. On the other hand, the SnRK2 OST1 interacts with regulatory PP2AA- and PP2AB’-subunits and pp2aa regulatory subunit double mutants show reduced ABA sensitivity in stomatal closure, although pp2a catalytic subunit double mutants show enhanced ABA-dependent SnRK2 activation 21 .…”

Type one protein phosphatases (TOPPs) contribute to the plant defense response in Arabidopsis

“…Previous studies have demonstrated that PP1 participates in gibberellin, ABA and auxin signaling as well as photomorphogenesis (Qin et al 2014;Guo et al 2015;Hou et al 2016;Yue et al 2016). Recent work showed that AUN1 (TOPP9) and AUN2 (TOPP8) negatively regulate cell wall integrity maintenance during tip growth (Franck et al 2018).…”

GardeniajasminoidesEncodes an Inhibitor-2 Protein for Protein Phosphatase Type 1

“…At inhibitor-2). Supporting a negative role of TOPP1 and AtI-2 in ABA signaling, topp1 and atI-2 mutant plants displayed hypersensitivities to ABA and salt treatments [12].…”